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Qualitative Analysis & Tests for Ions

Ready to testThe sample contains no precipitate yet. Add a few drops of NaOH.
VIRTUAL EXPERIMENTcation test with NaOH(aq)SAMPLE UNDER TESTFe2+aqueous cationNaOHOBSERVATIONReady to testbefore adding NaOHADD REAGENTA few dropsform the hydroxideAdd in excesstest its solubility
Practical method
  1. Place the unknown cation solution in a clean test tube.
  2. Add aqueous sodium hydroxide drop by drop and observe.
  3. Add excess NaOH to test whether the precipitate dissolves.
  4. For NH₄⁺, warm gently and test the gas with damp red litmus paper.
Cation sampleFe2+
NaOH addedNone yet
ObservationReady — no reaction yet
Soluble in excessNot applicable
Choose the cation sample

Safety: Sodium hydroxide is corrosive. Wear eye protection, use a test-tube rack, and never smell ammonia directly—waft only when instructed.

  • Test Ca2+ with a few drops of NaOH — confirm a white precipitate forms
  • Find the cation that gives a BLUE precipitate with NaOH
  • Find a cation whose white precipitate DISSOLVES when NaOH is added in excess
  • Confirm that Fe3+'s red-brown precipitate does NOT dissolve, even in excess NaOH
  • Test NH4+ — confirm no precipitate forms, but ammonia gas is produced instead